Development and Validation of a Monte Carlo Beam Model for 6, 8, and 15 MV Clinical Photon Beams on the Elekta™...

This study investigates a single-source photon beam model and a single source for contamination electrons for Monte Carlo (MC) simulations. Our approach uses a beam characterization model-to-model clinical photon beams for 6, 8, and 15 MV on a linear accelerator. The flattening filter attenuates the photon fluence in the beam model before reaching the secondary collimation accessories. An error function was used to model scatter from these devices. This study aimed to develop a model for clinical X-ray source beams for MC dose calculations for an Elekta^TM Precise Linac.

The photon energy was modeled with the Schiff formula and off-axis beam softening. DOSXYZnrc was used to calculate X-ray dose distributions in water and RW3 solid water phantoms. These distributions were compared to measured EBT3 film or water tank dose data. A gamma (γ) index was calculated to compare the MC and the measured dose. The criteria for the γ-index were 2% dose/2 mm distance-to-agreement. Dose distribution data for square, rectangular, offset, and irregular fields were compared with measurements.

A range of fields for 6, 8, and 15 MV beams was modeled, simulated, and compared to corresponding measured water tank data. Rectangular, small, and medium-sized offset fields met the γ-index criteria of 2%/2 mm.

The beam characterization model performed well against measured data and can be employed for dose verification ranging from regular fields to conformal treatments, as demonstrated by various multi-leaf collimator shapes.